IJCST 23,4. Youjiang Wang School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA

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1 The current issue and full text archive of this journal is available at IJCST 242 Utilization of recycled post consumer carpet waste fibers as reinforcement in lightweight cementitious composites Mehmet Ucar Mechanical Engineering Department, Kocaeli Universty, Kocaeli, Turkey, and Youjiang Wang School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA Abstract Purpose A large amount of post-consumer carpet waste is discarded into landfills. The need to recycle this waste is increasing due to the lack of available landfill spaces in many parts of the world, environmental concerns, and resource conservation. The purpose of this paper is to explore the use of this waste for a low-cost, high-volume application. Design/methodology/approach Fibers from carpet waste have been successfully used as reinforcement in concrete, typically at.1-1 per cent volume fraction (fractions by weight are even lower), for enhanced toughness. In this study, lightweight cementitious composites were fabricated that were reinforced with recycled carpet fibers at up to 2 per cent fiber to cement weight ratios. Flexural, toughness, and impact properties of the lightweight cementitious composites were characterized. Findings The density of the composites decreases with the increase of fiber content. In the three-point bending test, lightweight cementitious composites exhibited a ductile behavior, and the flexural strength increases with the density of the composites. The energy absorption measured by the drop weight impact test was not very sensitive to the material parameters due to the total absorption of the impact energy by the specimens. Originality/value The density of the lightweight composites ranges from.7 to 1. g/cm 3, which was about 3-4 per cent of the density of typical concrete. Besides being moisture and termite resistant, the lightweight composites were very tough and could be cut and fastened with ordinary tools and nails. The lightweight composites are suitable for applications such as underlayment and wall panels for buildings, as well as for outdoor structures. Keywords Construction materials, Reinforcement, Composite materials, Textile fibres, Recycling Paper type Research paper International Journal of Clothing Science and Technology Vol. 23 No. 4, 211 pp q Emerald Group Publishing Limited DOI 1.118/ Introduction World fiber production has been steadily increasing in the past few decades, now exceeding 64 million tons per year. In the USA alone, about 11.9 million tons of textile waste was generated, accounting for 4.7 wt% of the total municipal solid waste, and 15.9 per cent of textile waste was recovered in 27 (US Environmental Protection Agency (USEPA), 28). The outlets of the recovered textile waste include reuse, material recycling, and energy recovery. To enhance the environmental benefits of recycling, more effort is needed on research and development for better technologies that are cleaner, more energy efficient, and less expensive. Considering the diversity

2 of fibrous waste and structures, many technologies must work in concert in an integrated industry in order to have any noticeable impact on fibrous waste recovery (Wang, 21). Most of the fibrous waste is composed of natural and synthetic polymeric materials such as cotton, wool, silk, polyester, nylon, polypropylene, etc. Frequently, different types of polymers and other materials are integrated to form an article, such as blended textiles, carpet, conveyer belts, composites, to name a few. Post consumer carpet provides an example of complex materials systems that are very difficult to recycle. However, since carpet is more consistent in structure and material composition than most other single fibrous products, and because of the large volume of carpet waste, significant effort has been devoted to carpet waste collection and recycling. The US carpet industry consumes about 1.4 million tons of fibers per year, including nylon (6 per cent), polyolefin (29 per cent), polyester (1 per cent), and wool (.3 per cent). Among the nylon face fiber, about 4 per cent is nylon 6 and 6 per cent is nylon 6,6. The type of carpet is classified according to the type of face fibers used. A nylon 6 carpet, for instance, contains not only nylon 6 face fibers but also backing fibers (polypropylene) and adhesive (latex and filler). About 7 per cent of the carpet produced is for replacing old carpet, typically after 5-1 years of service. The rate of carpet disposal is about 2-3 million tons per year in the USA (Carpet America Recovery Effort (CARE), 26), and about 4-6 million tons per year worldwide. The tufted structure (Figure 1) is the most common type of carpet with a 9 per cent market share. It typically consists of two layers of backing (mostly polypropylene fabrics), joined by CaCO 3 -filled styrene-butadiene latex rubber (SBR), and face fibers (majority being nylon 6 and nylon 6,6 textured yarns) tufted into the primary backing. The SBR adhesive is a thermoset material, which cannot be remelted or reshaped. The compositions of typical carpet waste are shown in Figure 2. In a fiber recycling industry capable of processing a large amount of the waste discarded, a collection network is needed to provide sufficient and consistent supply of post consumer fiber waste at reasonable cost. Some technologies such as nylon 6 depolymerization can convert waste into desirable products, but they are only limited to certain types of waste such as nylon 6 carpet. Other technologies must coexist so that most of the waste collected can be utilized for profitable recycling, without quickly saturating any market of a product or having to discard some of the waste into landfills. As the past experience has shown, it cannot be economically competitive if only a fraction of the carpet waste collected can be recycled, while the rest has to be sent back to landfills. Many technologies are available and more are being developed to recycle fibrous waste (Wang, 26, 21). Using carpet waste fibers to make cement boards has been investigated in this study. To convert carpet waste into fibers for cement boards, only simple shedding Recycled carpet waste fibres 243 Face yarn (nylon etc) Primary backing (PP) Adhesive (CaCO 3 /latex) Secondary backing (PP) Figure 1. Tufted carpet structure

3 IJCST Face yarn 1291 Backing Figure 2. Typical carpet composition SBR CaCO 3 Adhesive layer (g/cm 2 ) is needed, avoiding expensive component identification and separation. Even unidentified waste stream and residue from many other recycling processes can be used. The overall process is low-cost and the market for the product is very large. 2. Lightweight cement board The lightweight cement boards developed in this study have a very high-fiber content, up to 2 wt% and are very light in weight (.7-1. g/cm 3 ) with a porous structure. In comparison, the typical concrete has a density of 2.4 g/cm 3 and the typical lightweight concrete has a density of 1.7 g/cm 3. The lightweight cement boards developed in this study can be easily cut with ordinary tools and they work well with nails and screws. The lightweight cement boards are prepared using fibers from post consumer carpet containing nylon and polypropylene fibers after coarse shredding. Fiber length ¼ 5-7 mm, and Portland cement: gray and white. Sample preparation involves the following steps: (1) cement, fibers and water are mixed in a container; (2) placed in a mold by hand; (3) allowed to cure for seven days; and (4) cut with ordinary saw for testing. Table I illustrates the fiber/cement/water ratios of the samples prepared and their densities. It is noted that density decreases with increase in fiber content, and it increases with increase in cement content. Weight ratios Sample no. Fiber Water Cement Density (g/cm 3 ) Table I. Fiber/cement/water ratios and density (gray) (gray) (gray) (gray) (white) (white) (white) 1.1

4 3. Flexural properties The flexural properties of the lightweight cement boards are measured in a three-point bending on an Instron machine. The specimens are about 3 mm in height. The test configuration is shown in Figure 3. Five specimens are tested for each sample. Typical test curves are shown in Figure 4. The flexural test specimens failed in a ductile mode. To characterize the toughness characteristics, toughness index (TI 5 ) is used, which is shown in Figure 5. For brittle material, TI 5 ¼ 1, for elastic-plastic materials, TI 5 ¼ 9, and for strain softening materials, TI 5 is between 1 and 9. The toughness index values for the test samples are summarized in Table II, from which is can be observed that all the samples show Recycled carpet waste fibres 245 Load (mm) Figure 3. Three-point flexural test configuration 1.5 Fiber/cement ratio Stress (MPa) Strain Figure 4. Typical flexural test curves (gray cement specimens) Stress TI 5 = A+B A A d B 5d Strain Figure 5. Definition of toughness index

5 IJCST similar toughness index values and their behavior is close to that of an elastic-plastic materials. Figure 6 shows that the flexural strength and modulus of the samples decrease with the fiber to cement ratio Impact properties The impact test is performed on an Instron Dynatub tester. The impact velocity is 2.15 m/s. The specimen dimensions are (thickness) mm. Weight ratios Sample no. Fiber Water Cement TI 5 Table II. Flexural toughness index (gray) (gray) (gray) (gray) (white) (white) (white) 7.5 Strength (MPa) Modulus (MPa) (a) Figure 6. Flexural test results (b) Notes: (a) Strength; (b) modulus vs fiber to cenent ratio

6 Energy absorption and maximum force are recorded. Figure 7 shows that the impact energy is not sensitive to the fiber to cement ratio. This is due to the total absorption of the impact energy at the test level by the specimens, as most damages are not visible from the backside. The maximum impact force, however, decreases with the fiber to cement ratio and increases with the density of the samples (Figure 8). 5. Summary A large amount of fibrous waste is disposed in landfills each year. This not only poses economical and environmental concerns to the society but also represents a waste of resources. In this study, lightweight cement boards are developed. Their characteristics include: lightweight, tough, easy to handle and install, moisture, mold, and termite resistant. This method of fiber recycling may work together with other technologies to maximize the use of waste collected. This method of recycling only requires simple shedding, thus avoiding expensive component identification and separation. Even unidentified waste stream and residue from many other recycling processes can be used. The overall process is low-cost and the market for the product is very large. Potential applications include underlayment board for tiles, wall panels replacing dry wall for wet locations, and outdoor patio tiles and stones. Recycled carpet waste fibres Energy (J) Figure 7. Impact energy vs fiber to cement ratio Maximum force (kn) Figure 8. Impact force vs fiber to cement ratio and specimen density

7 IJCST 248 References CARE (26), 25 Annual Report, Carpet America Recovery Effort, Dalton, GA, available at: USEPA (28), Municipal solid waste in the United States: 27 facts and figures, EPA53-R-8-1, USEPA, Washington, DC, p. 177, available at: Wang, Y. (26), Carpet recycling technologies, in Wang, Y. (Ed.), Recycling in Textiles, Woodhead Publishing, Cambridge, pp Wang, Y. (21), Fiber and textile waste utilization, Waste and Biomass Valorization, Vol. 1 No. 1, pp Corresponding author Youjiang Wang can be contacted at: youjiang.wang@mse.gatech.edu To purchase reprints of this article please reprints@emeraldinsight.com Or visit our web site for further details: